Viruses have been shown to cause a growing number of clinically significant human diseases. These include influenza virus, the herpes viruses (herpes simplex virus type I and type II (HSV-I and -II), cytomegalovirus (CMV), Epstein-Barr virus (EBV), and Varicella zoster (VZ)), hepatitis B virus (HBV), adenovirus, rotavirus, respiratory syncytial virus, polio virus, and measles virus.
Human retroviruses are now also known, the first of these having been obtained from a patient with cutaneous T cell lymphoma (Poiesz et al., PNAS 77:7415, 1980) and named Human T Cell Leukemia/Lymphoma Virus type I (HTLV I). Subsequently, a second human retrovirus, designated HTLV II, was isolated from a T cell variant of hairy cell leukemia (Kalyanaraman et al. Science 218:571, 1982). More recently the etiologic agent of Acquired Immune Deficiency Syndrome (AIDS) has been shown to be a retrovirus, variously designated Lymphadenopathy Associated Virus (LAV; Barre-Sinoussi et al., Science 220:868, 1983) , Human T-Cell Lymphotropic Virus III (HTLV III; Popovic et al., Science 224,:497, 1984), or AIDS Related Virus (ARV; Levy et al., Science 225:840, 1984). There is also evidence that non-A non-B hepatitis (NANB) may be caused by a retrovirus (Seto et al., Lancet ii:941, 1984; Iwarson et al., J. Med. Virol. 16:37, 1985).
Laboratory diagnosis of a viral infection can involve either detection of the virus itself or its components, or detection of the host's immune response to the virus (serologic detection). Depending upon the nature of the virus, detection of the virus itself or its components, by culture or by direct diagnosis, may be difficult or impossible. For example, although retroviruses cause persistent infections in animals, including man, retroviral antigens are not always readily detectable in the infected animal (Zagury et al., Science 226:449, 1984). For such viruses, serologic detection may be preferable to direct detection.
Serologic diagnosis of a viral infection requires a source of viral protein with which patient sera can be reacted to determine the presence or amount of antibody to the viral agent of interest. Typically, the virus is grown in a human cell line from which it can be purified by methods well known in the art. Many viruses, including the Herpes viruses, polio and measles virus, are cultivated in human diploid fibroblast lines, such as MRC5 or W138, (Smith in Diagnosis of Viral Infection, Lenette et al., Eds., Baltimore: University Park Press, 1979, pg.33). HTLV-I and -II are cultivated in continuous T cell lines, such as HUT-102 (Gazdan et al., Blood 55:409, 1980; Poiesz et al., supra). LAV can be cultivated in B lymphoblastoid cell lines (Montagnier et al., Science 225:62, 1984 ) or in certain continuous T cell lines, such as the H9 cell line described by Popovic et al., supra. There have been conflicting reports concerning the ability of CEM cells to be infected by LAV. Barre-Sinoussi et al. (supra) were unsuccessful in transmitting LAV to CEM. However, Cheingsong-Popov et al. (Lancet i:477, 1984) and Folks et al. (PNAS (USA) 82:4539, 1985) have described the infection of CEM or HAT-sensitive CEM derivatives with LAV.
A number of viruses are known to be transmissible through blood products (blood, blood serum, blood plasma and fractions thereof) making it important to screen the blood products to determine if the donor has been exposed to the virus. Screening can take the form of direct antigen detection (HBV/hepatitis), or detection of antibody to the virus (LAV/AIDS). Detection of antibody to the virus can be accomplished in any of several ways, including enzyme-linked immunosorbent assay (ELISA). Individuals whose blood contains antibodies to the viral agent of interest are said to be seropositive. Blood from seropositive donors is eliminated from the blood supply upon detection, thereby helping to prevent the spread of disease.
When ELISA based screening methods are used for the detection of anti-viral antibody, the incidence of false positives can be relatively high. Recent data on the use of ELISA screening assays for the detection of antibodies to LAV suggests that the problem is due, at least in part, to the presence of antibodies in donor blood to human class II histocompatibility antigens. These antibodies react with antigens from the cells (H9) in which the virus was cultivated (Schorr et al., New. Eng. J. Med. 313:384, 1985) .
The major histocompatibility complex (MHC) in man is denoted HLA and is encoded by a series of linked loci located on the short arm of chromosome 6. Class I HLA antigens are encoded by the HLA-A,B and C loci, while class II antigens are encoded by the HLA-DR, DP and DQ loci. Class I HLA antigens are expressed on virtually all nucleated cells, while class II antigens are found primarily on cells of the immune system. The HLA antigens are highly polymorphic, i.e., there is a large number of alleles at each locus, hence it is not uncommon to encounter antibodies to HLA antigens in the sera of individuals who have been exposed to cells from other individuals, for example, in persons who have been multiply transfused or who have had multiple pregnancies. In fact, sera from such individuals are presently used as sources of antibody for HLA typing purposes.
Due to incidence of false positives in current screening methods, there is a need in the art for cell lines which are suitable for cultivation of human viruses, yet which cell lines do not possess surface antigens which can elicit false positive reactions in serologic assays. The present invention fulfills this need and further provides other related advantages.